Design and Implementation of an Electrical Characterization System for Membrane Capacitive Deionization Units for the Water Treatment - MDPI
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membranes
Article
Design and Implementation of an Electrical Characterization
System for Membrane Capacitive Deionization Units for the
Water Treatment
Federico A. Leon * , Alejandro Ramos-Martin and David Santana
Departamento de Ingeniería de Procesos (Process Engineering Department), Campus de Tafira,
Universidad de las Palmas de Gran Canaria (University of Las Palmas de Gran Canaria),
35017 Las Palmas de Gran Canaria, Spain; alejandro.ramos@ulpgc.es (A.R.-M.);
david.santana122@alu.ulpgc.es (D.S.)
* Correspondence: federicoleon@perezvera.com; Tel.: +34-686-169-516
Abstract: The desalination of seawater is one of the most established techniques in the world. In the
middle of the 20th century this was achieved using water evaporation systems, later with reverse
osmosis membranes and nowadays with the possibility of capacitive deionization membranes.
Capacitive deionization and membrane capacitive deionization are an emerging technology that
make it possible to obtain drinking water with an efficiency of 95%. This technology is in the
development stage and consists of porous activated carbon electrodes, which have great potential
for saving energy in the water desalination process and can be used for desalination using an
innovative technology called capacitive deionization (CDI), or membrane capacitive deionization
(MCDI) if an anion and cation membrane exchange is used. In this paper is proposed and designed a
characterization system prototype for CDI and MCDI that can operate with constant current charging
Citation: Leon, F.A.; Ramos-Martin, and discharging (galvanostatic method). Adequate precision has been achieved, as can be seen in
A.; Santana, D. Design and
the results obtained. These results were obtained from the performance of typical characterization
Implementation of an Electrical
tests with electrochemical double layer capacitors (EDLC), since they are electrochemical devices that
Characterization System for
behave similarly to MCDI, from the point of view of the electrical variables of the processes that take
Membrane Capacitive Deionization
place in MCDI. A philosophy of using free software with open-source code has been followed, with
Units for the Water Treatment.
Membranes 2021, 11, 773. https://
software such as the Arduino and Processing programming editors (IDE), as well as the Arduino
doi.org/10.3390/membranes11100773 Nano board (ATmega328), the analogical-digital converter (ADC1115) and the digital-analogical
converter (MCP4725). Moreover, a low-cost system has been developed. A robust and versatile
Academic Editor: Jianhua Zhang system has been designed for water treatment, and a flexible system has been obtained for the
specifications established, as it is shown in the results section.
Received: 16 September 2021
Accepted: 5 October 2021 Keywords: membranes; capacitive deionization; reverse osmosis; desalination
Published: 11 October 2021
Publisher’s Note: MDPI stays neutral
with regard to jurisdictional claims in 1. Introduction
published maps and institutional affil-
The desalination of seawater is one of the most established techniques in the world.
iations.
In the middle of the 20th century, this was achieved using water evaporation systems and
later with reverse osmosis membranes. However, the resulting high energy consumption,
generally through fossil fuels, has been an important issue to solve [1–4].
Modern times have introduced the possibility to transition from the use of reverse
Copyright: © 2021 by the authors. osmosis to capacitive deionization (CDI), or membrane capacitive deionization when
Licensee MDPI, Basel, Switzerland.
an anion and cation membrane exchange is used, which is a novel system still under
This article is an open access article
development that, in addition to removing salt from the water, allows for the storage of
distributed under the terms and
energy, similar to other electrochemical devices (batteries, supercapacitors, etc.) [5–8].
conditions of the Creative Commons
Currently, some media outlets are claiming that the current hydrological year is the
Attribution (CC BY) license (https://
driest hydrological year of the decade. In the last 12 months, the Spanish water reserve has
creativecommons.org/licenses/by/
4.0/).
decreased by a volume of water equivalent to that of the Ebro Basin (7511 hm3 of capacity).
Membranes 2021, 11, 773. https://doi.org/10.3390/membranes11100773 https://www.mdpi.com/journal/membranes
Membranes 2021, 11, 773 2 of 50
These phenomena are aggravated by the evident signs of climate change and, in coun-
tries such as Spain, by the advance of desertification processes in large areas, causing water
to become so much of an essential resource that it has become as precious a commodity as
oil [4].
Knowing that 97% of the planet’s water is salty, the desalination of brackish or marine
water (or seawater desalination) is one of the possible alternatives to mitigate the problem.
However, current desalination technologies, such as reverse osmosis and distillation present
a serious problem, which is the high energy consumption required to produce drinkable
water, as well as the problem of boron removal.
Capacitive deionization (CDI) is an emerging technology that makes it possible to ob-
tain drinking water with an efficiency of 95% [5–10]. This technology is in the development
stage and consists of porous activated carbon electrodes, which have great potential for
saving energy in the water desalination process and can be used for desalination using
an innovative technology called capacitive deionization (CDI) and membrane capacitive
deionization (MCDI). In CDI and MCDI, salt ions are removed from brackish water by ap-
plying a voltage difference between two porous electrodes in which the ions are temporarily
immobilized, and dissolved salts are removed from different types of water [6–9].
The design and implementation of a characterization system for capacitive deioniza-
tion units for water treatment was performed using types of water ranging from supply
water to water from industrial processes. Capacitive deionization has emerged over the
years as a robust, energy-efficient solution for water treatment [10–18]. It is an effective
technology for the desalination of water with low to moderate salt content [5].
The optimal operating regime is obtained for water with a salt concentration of slightly
less than 10 g/L [18]. Since the salt ions are minority compounds in the water, they can
be removed from the mixture with this technology. In contrast, other methods extract
the water phase from the salt solution. This technology also allows for the possibility of
integrating renewable energy sources and energy storage [6–10].
The main objective of this study was the design and implementation of an electrical
characterization system for capacitive deionization units in water treatment. The intention
was also to make use of this system to obtain results that will make it possible to analyze
the impact of this technique on different CDI and MCDI elements. The electrical characteri-
zation system of CDI and MCDI has been implemented before [11–13]. In more detail, the
objectives to be achieved are the following:
To study a control system with a microcontroller (ATmega328 MICROCHIP) that
will allow interaction, control, conditioning of different tests and data collection with
the medium.
For future implementations, to study the variation of the concentration as a result of
the influence of injecting energy into the system, being influenced by the pH of the solution,
temperature, conductivity, etc.
Analyze by numerical methods the variables involved in the system,
Develop a system capable of testing different situations that verify the tests described
in similar works of the field.
Establish a laboratory-scale electrochemical evaluation methodology for the electrical
characterization of CDI and MCDI.
In addition to the tests, the results obtained will be used to determine improvements
in active materials (activated carbon, carbon fibers, carbon aerogels, etc.) and the current
collectors that make up the electrodes.
The set of results generated will serve as didactic material to illustrate the influence of
the effects studied. This material will be useful for future students and teachers of degrees
and masters programs of different universities thanks to the research and improvements
on the CDI and MCDI units.
Membranes2021,
Membranes 2021,11,
11,773
x FOR PEER REVIEW 33ofof50
52
2.2. Materials
Materials and
and Methods
Methods
Compared to
Compared to the
the classical
classicalworking
workingmodesmodesofof thethe
20th century,
20th there
century, have
there beenbeen
have sev-
eral innovations and new technologies, such as ion exchange in the membrane
several innovations and new technologies, such as ion exchange in the membrane (see (see Figure
1) [14–18],
Figure and operational
1) [14–18], optimization
and operational in modes
optimization suchsuch
in modes as “stop-flow”
as “stop-flow”during ionion
during ex-
change [19], salt ratio upon voltage reversal [16], current constant during operation
exchange [19], salt ratio upon voltage reversal [16], current constant during operation [19], [19],
energyrecovered
energy recoveredfor fordesalination
desalinationin inrelation
relationto tocycling
cycling[20,21],
[20,21],flow
flowthrough
throughelectrostatic
electrostatic
wherewater
where waterisisdirectly
directlyfaced
faced through
through thethe electrostatic
electrostatic [22,23]
[22,23] andand flow
flow electrodes
electrodes based
based on
on suspended carbon
suspended carbon [24]. [24].
Figure 1. Capacitive deionization cell (CDI).
Figure 1. Capacitive
Regarding the deionization cell (CDI).
historical evolution of CDI and MCDI, a stage was defined before 1995,
when aerogel carbon was developed for CCD. The peons who worked with the desalination
conceptRegarding
called itthe historical evolution
“electrochemical waterofdemineralization”
CDI and MCDI, a and
stageitswas defined before
originators 1995,
were Blair,
when aerogel carbon was developed for CCD. The peons who worked with
Murphy and their colleagues, in the 1960s [25–28]. The basic standardized methods for the desalina-
tion concept called
supercapacitors haveit been
“electrochemical
used to study water demineralization”
the behavior of CDI and and its originators
MCDI were
[29–33]. These
Blair, Murphy and their colleagues, in the 1960s [25–28]. The basic standardized
methods are constant current charging and discharging, constant power cycling, cyclic methods
for supercapacitors
voltammetry have been usedimpedance
and electrochemical to study thespectrometry.
behavior of CDI andprocedures,
These MCDI [29-33]. andThese
the
methods are constant current charging and discharging, constant power cycling,
self-charging and self-discharging phenomena, will be classified into three typologies: cyclic
voltammetry
frequency, and electrochemical
dynamic impedance spectrometry. These procedures, and the
and energy characterization.
self-charging and self-discharging phenomena, will be classified into three typologies: fre-
quency,
2.1. dynamic
Frequency and energy characterization.
Characterization
The electrochemical impedance spectroscopy (EIS) method is used to characterize the
electrochemicalCharacterization
2.1. Frequency behavior of energy storage devices.
The electrochemical
This method has gained impedance
popularity spectroscopy (EIS) method
in the last decade, is used
especially to characterize
in the determination the
electrochemical
of the capacity inbehavior
fuel cellsof energy
and storage
batteries, duedevices.
to the development of the electric car [34,35].
The
Thispurpose
method of hasthe EIS ispopularity
gained to study the system
in the response
last decade, to the application
especially of a small
in the determination
amplitude periodic
of the capacity in fuelalternating current (AC)
cells and batteries, due tosignal. These measurements
the development of the electricare
carcarried
[34,35].
out atThedifferent
purpose frequencies,
of the EIS which is why
is to study theitsystem
is in the frequency
response characterization
to the application of agroup.
small
However, this technique is very sensitive, and it is essential to perform
amplitude periodic alternating current (AC) signal. These measurements are carried out it as accurately as
possible. Therefore, it is necessary to use several characterization techniques,
at different frequencies, which is why it is in the frequency characterization group. How- because there
isever,
no single techniqueisthat
this technique verygives all theand
sensitive, expected results.toComplementary
it is essential techniques
perform it as accurately are
as pos-
therefore used. it is necessary to use several characterization techniques, because there is
sible. Therefore,
On thetechnique
no single other hand, there
that areall
gives limitations
the expected at high frequencies
results. with CDI, due
Complementary to the low
techniques are
impedance that
therefore used. the CDI cell can present. One of the factors conditioning the impedance of
CDI is dissolution, while others are caused by coupling effects between the power supply
Membranes 2021, 11, 773 4 of 50
and the media system cables [36]. These adversities are limited to low frequencies. In
practice, twisted cables are used for the measurement cells to reduce these types of errors.
2.2. Dynamic Characterization
The constant current charge/discharge method is the simplest method to apply with
direct current (DC). It analyzes the response of CDI when a constant charge/discharge
current is applied to it. Despite being a basic method, it is widely used in the characteri-
zation of capacitors. Its application is documented with standardizations and will be the
main object of the characterization of CDI in this work, being the main endorsement of the
designed device [37–40].
The self-charging or self-discharging of CDI has its origin in two main causes. First,
when CDI is charged or discharged, there is a diffusion of ions from the solution to the
activated carbon electrode, or vice versa. The diffusion immediately after charging or
discharging causes a self-discharge or self-charge, respectively. Secondly, these phenomena
exist due to leakage current. Self-discharge by diffusion occurs predominantly in the initial
stage. However, self-discharge by leakage is significant after self-discharge begins [41].
Self-discharge originates during dynamic operation, e.g., the dynamic operating cycle of
electric vehicles [42], whose genome is through the equivalent impedance method, whose
phase element is constant.
On the other hand, we highlight cyclic voltammetry (C.V.), which has achieved the
distinction of a procedure used to evaluate the performance of energy storage systems,
as well as to determine the life cycle, the effects of internal resistance and the dissipation
losses [43]. The method consists of applying a linear voltage ramp and storing the current
response in the capacitors. This current is directly associated with the capacity of the
component achieving a versatile procedure [44–49].
Constant power cycling is known as “cycle life testing” (C.L.T.); it is a methodology
for calculating the electrochemical device parameter based on periodic charging and
discharging, separated by rest time intervals [50–53].
The procedure consists of charging the device at a given power until a voltage is
achieved [54–57]. Once this point is reached, the polarity of the current is reversed by
applying a given value, and the current is resumed by reversing the current, so that the
charging cycle is continued up to a higher voltage [45,46].
This is a research study in the industrial field and several milestones have been
previously established, which are as follows:
1. A device capable of characterizing capacitive deionization (CDI) and membrane
capacitive deionization (MCDI) for different tests, shown in Figure 2, in such a way
that the main characteristics of capacitive deionization can be obtained, such as
equivalent series resistance, capacitance, etc.
2. A system capable of collecting the test parameters and configuring it through a
graphical user interface (GUI).
3. A procedure capable of characterizing the CDI and MCDI for stationary flows.
4. The results obtained will be studied in future research lines for CDI and MCDI technology.
2.3. General Description of the System
Figure 2 shows the scheme of the characterization system prototype for capaci-
tive deionization (CSP-CDI), and the interrelation of components. These components
that make up this diagram define the fundamental structure of the system. It is briefly
explained below:
1. Control and data acquisition system (microcontroller ATmega328): this part of the
system can store data and control the different parameters of the CSP-CDI. This part
of the system can analyze the data in real time to actuate the power system. The
microcontroller ATmega328 model (Atmel, Beijing, China) is implemented in the
platform Arduino Nano (Arduino, Beijing, China). This microcontroller is responsible
Membranes 2021, 11, 773 5 of 50
for directly controlling the galvanostatic charging process, so as to capture the data
and send them to a PC for saving them (Appendix A shows the Arduino source code).
2. Power system (OPA549): A power operational amplifier OPA549 (Texas Instruments).
This operational amplifier can provide a nominal current of 8A and also has a special
input (ilim) for limiting the output current of the amplifier. This is an important
feature for implementing galvanostatic charge or discharge (by controlling the cur-
rent). This operational amplifier is responsible for sourcing the system, in order to
charge and discharge the CDI cell or other similar electrochemical devices (batteries,
electrochemical double layer capacitors, etc.).
3. ADS1015: An analogical-digital conversion stage based on the precision converter
ADS1015 (Texas Instruments, Shanghai, China). This stage has two differential analog
inputs for measuring: the charging or discharging current and the voltage of CDI cell.
Current i(t) is measured from the voltage of a resistor Rm = 0.1 Ω, which is arranged
between the output of the operational amplifier and CDI cell and the CDI cell voltage
v(t) directly. The circuit ADS1015 has a 12-Bit resolution, which sets a resolution of
3 mV for the voltage measuring and 30 mA for the current measuring.
4. MCP4725: Two digital-analogical conversion stages based on MCP4725 (MICROCHIP,
Beijing, China) with a resolution of 12 Bit. These stages are used to control the charg-
ing/discharging processes of EDLC, for setting the voltage and current intensity references.
5. A PC: that is responsible for controlling and configuring the microcontroller for
conducting the tests and storage of data obtained from the measurements. This
is achieved through a script made in JavaScript language under Processing IDE
(Processing Foundation). For the different tests, data were sent to the PC from
the microcontroller (ATmega328), where they were saved by means of the use of
Processing tool. At the Appendix B is showed the Processing source code, and
Figure 3 displays the control interface achieved with Processing, for being used at
the PC.
6. CDI cell: this is the object of study of this paper. Its correct operation is essential to
Membranes 2021, 11, x FOR PEER REVIEW characterize it. Its operating range has been designed to satisfy the needs required 5 ofin
52
the programmed tests, which have carried on with different EDLCs (electrochemical
double layer capacitors) for commissioning and evaluation.
Figure2.2.Scheme
Figure Schemeof
ofthe
thecharacterization
characterizationsystem
systemprototype
prototypefor
forcapacitive
capacitivedeionization
deionization(CSP-CDI).
(CSP-CDI).
2.3. General Description of the System
Figure 2 shows the scheme of the characterization system prototype for capacitive
deionization (CSP-CDI), and the interrelation of components. These components that
make up this diagram define the fundamental structure of the system. It is briefly ex-
plained below:
(Processing Foundation). For the different tests, data were sent to the PC from the
microcontroller (ATmega328), where they were saved by means of the use of Pro-
cessing tool. At the Appendix B is showed the Processing source code, and Figure 3
displays the control interface achieved with Processing, for being used at the PC.
6. CDI cell: this is the object of study of this paper. Its correct operation is essential to
Membranes 2021, 11, 773 characterize it. Its operating range has been designed to satisfy the needs required in 6 of 50
the programmed tests, which have carried on with different EDLCs (electrochemical
double layer capacitors) for commissioning and evaluation.
Figure 3.
Figure 3. −Processing
ProcessingPC
PCcontrol
control interface
interface and
anddata
datalogger.
logger. Comme
3.3. Results
Results
The target
The target prototype
prototype developed
developed for for characterization
characterizationtesting
testingisiscapable
capableofofcharging
charging and
discharging at constant voltage and current (galvanostatic mode). InInaddition,
and discharging at constant voltage and current (galvanostatic mode). addition,the
thepower
power supply provides the load with a constant current at 95% efficiency
supply provides the load with a constant current at 95% efficiency and establishes the and establishes
the duration
duration for which
for which thethe nominal
nominal voltage
voltage is ismaintained.
maintained.The The device
device isis capable
capableofofmeas-
measuring
uring current and voltage with a maximum error tolerance of ±
current and voltage with a maximum error tolerance of ±1%. Moreover, voltmeter 1%. Moreover, voltmeter mea-
measurements
surements havehave a resolution
a resolution of of 0.125
0.125 mVmVfor forvoltage
voltagemeasurement.
measurement. The Theinput
inputimped-
impedance
ance of these voltmeters must be sufficiently high for measurement errors to be negligible.
of these voltmeters must be sufficiently high for measurement errors to be negligible. To
To obtain the data, an analog-digital converter (ADC1115) was used, which has a series of
obtain the data, an analog-digital converter (ADC1115) was used, which has a series of
filters at the input and output of the converter, resulting in precise, noise-free data.
filters at the input and output of the converter, resulting in precise, noise-free data.
The designed device must be able to perform constant voltage and current charging
The designed
and discharging, device
as well must be ablevoltage
as simultaneous to perform constant
and current voltage and
measurements current
at the termi-charg-
ing and discharging,
nals of the CDI cell. as well as simultaneous voltage and current measurements at the
terminals of the CDI cell.
The power supply (through the OPA549) must be able to provide the constant load
Thetopower
current the CDIsupply
cell with(through the OPA549)
95% efficiency must beset
and, in addition, able
theto provide
duration of the constant
voltage
load current
maintenance. to the CDI cell with 95% efficiency and, in addition, set the duration of
voltage maintenance.
The developed device must satisfy the requirement of an error tolerance of ± 0.01%
The developed
for voltage measurement device
andmust satisfy
an error the requirement
tolerance of ± 0.1% for of an error
current tolerance of ± 0.01%
measurement.
for voltage measurement and an error tolerance of ±0.1% for current measurement.
3.1. Proposed Test Results
3.1. Proposed Test provides
This section Results the details of the tests carried out and the results obtained for
the characterization of the CCD
This section provides the system.
details of the tests carried out and the results obtained for
the characterization of the CCD system.
3.1.1. Calibration of the Equipment
3.1.1. Calibration of the Equipment
To provide veracity and reliability to the results obtained during the tests, the CSP-CDI
was first subjected to a series of calibration tests. The procedure that followed consisted in
the fact that, knowing an input setpoint, the system returned a series of expected results
since the output data were known, since a 1 Ω resistor was used instead of a CDI cell.
Calibration of the Digital-to-Analog Converter DAC (MCP4725)
The first test of the CSP-CDI was the calibration of the equipment by setting an input
setpoint current to measure the voltage at the terminals of the 1 Ω resistor (see the results
in Table 1). With this experience, the calibration line of the equipment is determined,
obtaining the expression of the digital-analogical converter’s transformation of accounts.
Membranes 2021, 11, 773 7 of 50
Table 1. Calibration of the system in the digital-analog converter (MCP4725).
Ic (mA) Measures (mA)
−138.890 −142.1
−13.889 −10.6
−1.3889 2.1
0 3.9 Test 1
1.3889 5.6
13.889 18.7
138.890 151.5
−138.890 −143.1
−13.889 −10.5
−1.3889 2.4
0 3.6 Test 2
1.3889 5.3
13.889 18.6
138.890 151.4
−138.890 −142.9
−13.889 −10.5
−1.3889 2.3
0 3.7 Test 3
1.3889 5.4
13.889 18.6
138.890 151.4
As can be seen in the previous Figure 4, the slope of the straight line corresponds to
the resistance of 1 Ω, and it can also be seen that the data dispersion is null, so the sample
taken refers to the population and indicates that the CSP-CDI is characterized with the
Equation (1):
y = 1.0588 X + 3.9833 (1)
where:
X is the rated setpoint current in mA (milli-Amperes).
Membranes 2021, 11, x Y isPEER
FOR the REVIEW
current at the load mA (milli-Amperes). 8 of 52
Finally, knowing the current, the voltage is trivial because the resistance is 1 Ω.
Calibration line
200 y = 1.0588x + 3.9833
150
100
50
Calibration line
Line (Calibration line)
-100
-150
-200
Figurewith
Figure 4. DAC calibration 4. DAC calibration
the load with the load resistance.
resistance.
Calibration
Calibration of the of the Analogical-Digital
Analogical-Digital ConverterConverter (ADS1115)
(ADS1115)
This experimentThisisexperiment
based onisconnecting
based on connecting a 1 Ω (Ohms)
a 1 Ω (Ohms) resistor
resistor to to theload
the load and
and estab-
es-
lishing an input setpoint current to measure the voltage in the measuring cell. With this,
tablishing an input setpoint current to measure the voltage in the measuring cell. With
we know the current and current of the CSP-CDI (see Figures 5–8). With this experience,
the calibration line of the equipment is determined, obtaining the expression of the trans-
formation of accounts of the analogical-digital converter (table 2).
Membranes 2021, 11, 773 8 of 50
this, we know the current and current of the CSP-CDI (see Figures 5–8). With this experi-
ence, the calibration line of the equipment is determined, obtaining the expression of the
transformation of accounts of the analogical-digital converter (Table 2). 9 of 52
Membranes 2021, 11, x FOR PEER REVIEW
Table 2. Calibration of the system in the analog-digital converter (ADS1115).
Table 2. Calibration of the system in the analog-digital converter (ADS1115).
V_Sensor I_Sensor V_Count_Measures I_Count_Measures Sample
V_Sensor
0.860 I_Sensor
0.091 V_Count_Measures
6892 I_Count_Measures
735 Sample
0.860
0.816 0.091
0.757 6892 6527 735 6060
0.816
0.713 0.757
2.292 6527 5710 6060 18,365
0.713
0.698 2.292
2.515 5710 5591 18,365 20,152
0.698 2.515 5591 5578 20,152 20,354 Measure 1
0.696 2.541
Measure 1
0.696
0.695 2.541
2.563 5578 5565 20,354 20,535
0.680
0.695 2.784
2.563 5565 5450 20,535 22,302
0.597
0.680 4.020
2.784 5450 4785 22,302 32,260
0.597
0.860 4.020
0.090 4785 6889 32,260 730
0.860
0.814 0.090
0.760 6889 6524 730 6090
0.814
0.713 0.760
2.290 6524 5710 6090 18,346
0.713
0.698 2.290
2.515 5710 5592 18,346 20,142
0.698 2.515 5592 5578 20,142 20,358 Measure 2
0.696 2.542 Measure 2
0.696
0.695 2.542
2.565 5578 5565 20,358 20,542
0.695
0.680 2.565
2.783 5565 5450 20,542 22,290
0.680
0.597 2.783
4.020 5450 4785 22,290 32,261
0.597 4.020 4785 32,261
0.860 0.090 6887 730
0.860
0.814 0.090
0.761 6887 6524 730 6100
0.814
0.713 0.761
2.292 6524 5710 6100 18,362
0.713
0.698 2.292
2.515 5710 5592 18,362 20,145
0.698 2.515 5592 5577 20,145 20,366 Measure 3
0.696 2.543 Measure 3
0.696
0.695 2.543
2.565 5577 5567 20,366 20,546
0.695
0.680 2.565
2.783 5567 5450 20,546 22,290
0.680
0.597 2.783
4.020 5450 4786 22,290 32,260
0.597 4.020 4786 32,260
I_count_measures (ADC)
45000
40000
35000
30000
25000
20000 I_count_measures
Line (I_count_measures)
5000
-0.2 -0.15 -0.1 -0.05 0 0.05 0.1 0.15 0.2
A (Amps)
Figure 5.5.“I”
Figure “I”counts measured
counts at theatADC.
measured the ADC.
Membranes 2021, 11, 773 9 of 50
Membranes 2021, 11, x FOR PEER REVIEW 10 of 52
Membranes 2021, 11, x FOR PEER REVIEW 10 of 52
y = 17.691x + 2.5387
5 y = 17.691x + 2.5387
5
3
I_Sensor
3
I_Sensor
Line (I_Sensor)
Line (I_Sensor)
-0.2 -0.15 -0.1 -0.05 0 0.05 0.1 0.15 0.2
-0.2 -0.15 -0.1 -0.05 0 0.05 0.1 0.15 0.2
A (Amps)
A (Amps)
Figure 6. Intensity at the sensor.
Figure 6. Intensity at the sensor.
Figure 6. Intensity at the sensor.
V_counts_measures (ADC)
8000 V_counts_measures (ADC)
8000 y = -9466.1x + 5577.9
7000 y = -9466.1x + 5577.9
7000
5000
5000
4000
V_count_measures
4000
3000 V_count_measures
Line (V_count_measures)
3000
2000 Line (V_count_measures)
2000
1000
1000
-0.2 -0.15 -0.1 -0.05 0 0.05 0.1 0.15 0.2
-0.2 -0.15 -0.1 -0.05 0 0.05 0.1 0.15 0.2
A (Amps)
A (Amps)
Figure 7. “V” counts measured on the ADC.
Membranes 2021, 11, x FOR PEER REVIEW 11 of 52
Figure 7. “V” counts measured on the ADC.
Figure 7. “V” counts measured on the ADC.
1
0.9
0.8 y = -1.1824x + 0.6963
0.7
0.6
0.5
0.4
Line (V_sensor)
0.3
0.2
0.1
-0.2 -0.15 -0.1 -0.05 0 0.05 0.1 0.15 0.2
A (Amps)
Figure 8. Voltage at the sensor.
Figure 8. Voltage at the sensor.
As can be seen in the previous figures, the data dispersion is null, so the sample taken
refers to the population and indicates that the CSP-CDI is characterized, with Equation (2)
being “I” of the measured ADC counts, while Equation (3) is the sensor current, Equation
(4) is “V” of the measured ADC counts, and Equation (5) is the sensor voltage, as follows:
Membranes 2021, 11, 773 10 of 50
As can be seen in the previous figures, the data dispersion is null, so the sample taken
refers to the population and indicates that the CSP-CDI is characterized, with Equation (2)
being “I” of the measured ADC counts, while Equation (3) is the sensor current, Equation
(4) is “V” of the measured ADC counts, and Equation (5) is the sensor voltage, as follows:
y = 141704 X + 20340 (2)
where:
X is the rated set point current in A (Amps).
Y are the counts corresponding to the current of the ADS1115.
y = 17.691 X + 2.5387 (3)
where:
X is the rated setpoint current in A (Amperes).
Y is the measured current in V (Volts) at the sensor.
y = −9466.1 X + 5577.9 (4)
where:
X is the rated setpoint current in A (Amperes).
Y are the counts corresponding to the voltage of the ADS1115.
y = −1.1824 X + 0.6963 (5)
where:
X is the rated setpoint current in A (Amperes).
Y is the measured voltage in V (Volts) at the sensor.
3.1.2. Charging and Self-Discharge Tests at an Input Set Point
This section specifies the tests to which the equipment is subjected for its validation,
where the degree of response from the equipment to an input setpoint will be determined,
characterizing its behavior through the supercapacitors and the standardized tests.
Three samples were taken in each test to avoid uncertainty and mean error. Further-
more, the data obtained in the tests are representative of the CSP-CDI.
The first characterization test performed was the charging and self-discharging of a
1 F capacity supercapacitor with a setpoint voltage of 2 V and a setpoint current of 0.1 A.
The data generated were stored in a database. The data generated have been saved in a
plain text file with “.txt” extension for further processing.
A script was created with Matlab software for data management on the screen. In this
way, a detailed analysis of each test carried out is carried out. The result of this first test
can be seen in Figure 9.
Figures 10–13 show that the test was carried out satisfactorily. Although, there is a
small variation of 0.01 A in the current. This was due to an equipment calibration problem,
hence the importance of having the CSP-CDI properly calibrated.The data generated were stored in a database. The data generated have been saved in a
plain text file with “.txt” extension for further processing.
Membranes 2021, 11, 773 A script was created with Matlab software for data management on the screen. In
11 of 50
this way, a detailed analysis of each test carried out is carried out. The result of this first
test can be seen in Figure 9.
Voltage
Intensity
Membranes 2021, 11, x FOR PEER REVIEW 13 of 52
Figure9.9 Charging
Figure Charging and
and self-discharge
self-discharge test
test at
at Vc_max
Vc_max == 22 V
V and
and Ic
Ic =
= 0.1
0.1 A.
A.
Figures 10–13 show that the test was carried out satisfactorily. Although, there is a
small variation of 0.01 A in the current. This was due to an equipment calibration problem,
hence the importance of having the CSP-CDI properly calibrated.
Figure10.
Figure 10.Charge
Chargeand
andself-discharge
self-dischargetest
test(voltage–current):
(voltage–current):Vc_max
Vc_max==22VVand
andIc
Ic== 0.1
0.1 A.
A.
The following tests were at the same maximum set point voltage, but at the set point
current of 0.05 A and 0.025 A, respectively. The following Figures 12 and 13 show the
results of the tests per screen.Figure 10. Charge and self-discharge test (voltage–current): Vc_max = 2 V and Ic = 0.1 A.
Membranes 2021, 11, 773 The following tests were at the same maximum set point voltage,12but at the set p
of 50
current of 0.05 A and 0.025 A, respectively. The following Figures 12 and 13 show
results of the tests per screen.
Membranes 2021, 11, x FOR PEER REVIEW 14 of 52
Figure
Figure 11. Load and11. Load and self-discharge
self-discharge test=at2 Vc_max
test at Vc_max V and Ic==20.05
V and
A. Ic = 0.05 A.
Voltage
Intensity
Figure12.
Figure 12.Charge
Chargeand
andself-discharge
self-dischargetest
testatatVc
Vcmax
max==22VVand
andIcIc==0.025
0.025A.
A.
On the other hand, the system was validated with another supercapacitor, with a
capacity of 650 F at another maximum voltage and setpoint current. The test results can
be seen in the following figure.
VoltageFigure 12. Charge and self-discharge test at Vc max = 2 V and Ic = 0.025 A.
Membranes 2021, 11, 773 On the other hand, the system was validated with another supercapacitor, 13with
of 50 a
capacity of 650 F at another maximum voltage and setpoint current. The test results can
be seen in the following figure.
Voltage
Intensity
Figure13.
Figure 13.Test
Testwith
witha a650
650FFsupercapacitor.
supercapacitor.
The following tests were at the same maximum set point voltage, but at the set point
current of 0.05 A and 0.025 A, respectively. The following Figures 12 and 13 show the
results of the tests per screen.
On the other hand, the system was validated with another supercapacitor, with a
capacity of 650 F at another maximum voltage and setpoint current. The test results can be
seen in the following figure.
Firstly, as can be seen in Figure 14, the test was carried out at the set voltage of 0.4 V
and set current of 0.1 A. This test lasted 1 h. It should be noted that the results are as
expected for a supercapacitor with these characteristics, the reason being that the setpoint
current is very small and the capacity of the supercapacitor is too large.
On the other hand, quality results have been obtained without the adverse effects of
noise. This was possible because the design of the CSP-CDI foresaw the need to have a
noise-free reading of the data when characterizing. For this reason, the use of the analogical-
to-digital converter (ADS1115) is fundamental to the system. This converter has a series of
input and output filters that result in accurate and noise-free data.
Finally, the self-discharge of CDI for 1 F, 100 F and 150 F supercapacitors has been
analyzed and characterized (Figures 11–14). The results shown are satisfactory and, with
this, the characterization system is again validated.
As can be seen in Figures 15 and 16, there are anomalies at the beginning of the
charge and self-discharge. It has been deduced from the results obtained that an equivalent
series resistance coexists due to the poor connection of the supercapacitor with the system
terminals, resulting in a series resistance of 56 Ω. This can be seen in more detail in
Figure 17.noise. This was possible because the design of the CSP-CDI foresaw the need to have a
noise-free reading of the data when characterizing. For this reason, the use of the analog-
ical-to-digital converter (ADS1115) is fundamental to the system. This converter has a se-
ries of input and output filters that result in accurate and noise-free data.
Membranes 2021, 11, 773 Finally, the self-discharge of CDI for 1 F, 100 F and 150 F supercapacitors has been
14 of 50
analyzed and characterized (Figures 11–14). The results shown are satisfactory and, with
this, the characterization system is again validated.
Voltage
Intensity
Membranes 2021, 11, x FOR PEER REVIEW 16 of 52
Figure14.
Figure 14.Self-discharge
Self-dischargetest
testtotocharacterize
characterizea a1 1F Fcapacitor.
capacitor.
As can be seen in Figures 15 and 16, there are anomalies at the beginning of the charge
and self-discharge. It has been deduced from the results obtained that an equivalent series
resistance coexists due to the poor connection of the supercapacitor with the system ter-
minals, resulting in a series resistance of 56 Ω. This can be seen in more detail in Figure
17.
Figure15.
Figure 15.Self-discharge
Self-dischargeanalysis
analysischaracterizing
characterizingaa100
100FFcapacitor.
capacitor.
Voltage
IntensityMembranes 2021, 11, 773 15 of 50
Figure 15. Self-discharge analysis characterizing a 100 F capacitor.
Voltage
Intensity
Membranes 2021, 11, x FOR PEER REVIEW 17 of 52
Figure16.
Figure 16.Charge
Chargeand
andself-discharge
self-dischargetest
testtotocharacterize
characterizeaa150
150FFcapacitor.
capacitor.
Figure 17. Graphs with details of the charge and self-discharge test, characterizing it on a 150 F
Figure 17. Graphs with details of the charge and self-discharge test, characterizing it on a 150 F capacitor.
capacitor.
3.1.3. CDI Charging and Discharging Test
In this section, the system will be validated based on the standardized tests for su-
percapacitors. For the first charge and discharge characterization test of the CSP-CDI, the
initial data have been programmed via the interface created with processing. The follow-Membranes 2021, 11, 773 16 of 50
3.1.3. CDI Charging and Discharging Test
In this section, the system will be validated based on the standardized tests for
supercapacitors. For the first charge and discharge characterization test of the CSP-CDI, the
initial data have been programmed via the interface created with processing. The following
table (Table 3) shows the data given to the interface.
Table 3. Data initially programmed in the processing interface.
Time 1 0.3 Minutes
Time 2 45 Seconds
Time 3 0.25 Hours
Time 4 45 Seconds
Time 5 0.25 Hours
Ic 01 A (Amperes)
Vcmax 1.8 V (Volts)
Capacitor capacity 1 F (Farads)
Once the data have been entered on the screen, the test is started. Once the test has
Membranes 2021, 11, x FOR PEER REVIEW
been completedand the data obtained have been managed, the result is shown on 18 the
of 52
screen (Figure 18).
Voltage
Intensidad
Figure18.
Figure 18.Charge
Chargeand
anddischarge
dischargetest
testatatVcmax
Vcmax==1.8
1.8VVand
andIcon
Icon==0.1
0.1A.
A.
Firstly,the
Firstly, thetest
testisissatisfactory.
satisfactory.Figure
Figure19
19shows
showseach
eachof
ofthe
thetimes
timesthat
thatmake
makeup
upthe
the
experiment,which
experiment, whichare:
are:time
timeone,
one,time
timetwo,
two,time
timethree,
three,time
timefour
fourand
andtime
timefive.
five.Figure 18. Charge and discharge test at Vcmax = 1.8 V and Icon = 0.1 A.
Membranes 2021, 11, 773 17 of 50
Firstly, the test is satisfactory. Figure 19 shows each of the times that make up the
experiment, which are: time one, time two, time three, time four and time five.
Figure19.
Figure 19.Detailed
Detailedgraphs
graphsfor
forthe
theloading
loadingand
andunloading
unloadingtest
testatatVcmax
Vcmax==1.8
1.8VVand
andIcon
Icon==0.1
0.1A.
A.
Secondly, the test responds to the initially programmed times and the input setpoints
(Vcmax and Icons).
Finally, the cleanliness of the data obtained should be highlighted, as the noise phe-
nomenon in the result is negligible. This has been possible with the analogical-digital
converter (ADS1115), which inhibits the noise generated by the instrumentation elements
of the system.
On the other hand, another test has been carried out with different initial conditions to
those described above, to validate the CSP-CDI system. The data entered by the interface
are shown in Table 4.
Table 4. Data programmed for the second loading and unloading test.
Time 1 0.3 Minutes
Time 2 45 Seconds
Time 3 0.1 Hours
Time 4 45 Seconds
Time 5 0.1 Hours
Ic 0.1 A (Amperes)
Vcmax 2 V (Volts)
Capacitor capacity 1 F (Farads)
The results per screen can be seen in Figure 20.
In Figure 20, it can be seen in time interval five that the capacitor self-charges once
this period starts. The cause is the inertia of the capacitor in maintaining an equilibrium
state, even though the attack current in the CSP-CDI system is 0A.
Finally, a new charge/discharge test is carried out with a supercapacitor of capacity 1
F (Farad), with different initial conditions to those previously described. The data initially
programmed by the interface are shown in the following Table 5.Ic 0.1 A (Amperes)
Vcmax 2 V (Volts)
Capacitor capacity 1 F (Farads)
Membranes 2021, 11, 773 The results per screen can be seen in Figure 20. 18 of 50
Figure 20. Charge and discharge test for the 1 F supercapacitor with other input setpoints.
Membranes 2021, 11, x FOR PEERFigure
REVIEW 20.
Charge and discharge test for the 1 F supercapacitor with other input
20 of 52 setpoints.
Table 5. Data programmed to characterize the CSP-CDI system.
In Figure 20, it can be seen in time interval five that the capacitor self-charges once
Table 5. Data programmed
Time 1 to characterize the CSP-CDI system. 1
this period starts. The cause is the inertia of the capacitor in maintainingMinutes an equilibrium
Time
1 2the attack current1 in the CSP-CDI
45 Seconds
state, even though
Time
Time
system is
Minutes 0A.
2 3 0.025 Hours
Finally,Time
a Time
new 45
4charge/discharge test is carried
45 out Seconds
with a supercapacitor
Secondsof capacity
Time 3 0.025 Hours
1 F (Farad),Time Timedifferent
with 5 initial conditions 0.025
to those previously described.Hours
The data ini-
4 45 Seconds
Ic 0.1 A (Amperes)
tially programmed
Time 5
Vcmax
by the interface are
0.025 shown 1
in the following
Hours Table 5. V (Volts)
Ic
Capacitor capacity 0.1 1 A (Amperes) F (Farads)
Vcmax 1 V (Volts)
Capacitor capacity 1 F (Farads)
The following Figures 21 and 22 show the results of the test per screen.
The following Figures 21 and 22 show the results of the test per screen.
Voltage
Intensity
Figure Charging
21. 21
Figure Chargingand
and discharging test
discharging test characterizing
characterizing a 1 F supercapacitor.
a 1 F supercapacitor.Membranes 2021, 11, 773 19 of 50
Membranes 2021, 11, x FOR PEER REVIEW 21 of 52
Figure
Figure 22.
22. Charge
Charge and
and discharge
discharge test at Vcmax == 11 V
V and
and Icon
Icon ==0.1
0.1A.
A.
4. Conclusions
4. Conclusions
The conclusions
The conclusions obtained
obtained in
in the
the development
development of
of this
this study
study are
are as
as follows:
follows:
1.
1. AAprototype
prototypehashasbeen
been designed
designed that
that can
can operate
operate with
with constant
constant current
current charging
charging and
and
discharging.
discharging.
2.
2. Adequateprecision
Adequate precisionhas
hasbeen
beenachieved,
achieved, as
as can
can be
be seen
seen in
in the
the results
results obtained.
obtained.
3.
3. A philosophy of using free software with open-source code has been
A philosophy of using free software with open-source code has been followed, followed, such as
such
the microcontroller ATmega328 (Arduino platform) and Processing programming
as the microcontroller ATmega328 (Arduino platform) and Processing programming ed-
itors, asas
editors, well asas
well the analogical-digital
the converter
analogical-digital converter(ADS1015)
(ADS1015) and thethe
and digital-analogical
digital-analog-
converter (MCP4725).
ical converter (MCP4725).
4. A low-cost system has been developed.
4. A low-cost system has been developed.
5. A robust and versatile system has been designed for water treatment.
5. A robust and versatile system has been designed for water treatment.
6. A flexible system has been obtained for the specifications established.
6. A flexible system has been obtained for the specifications established.
Contributions: Conceptualization,
Author Contributions:
Author F.A.L.,
Conceptualization, F.L., A.R.A.R.-M. andmethodology,
and D.S.; D.S.; methodology,
F.L. andF.A.L. and
A.R.; soft-
A.R.-M.; software, A.R.-M. and D.S.; validation, F.A.L., A.R.-M. and D.S.; formal analysis,
ware, A.R. and D.S.; validation, F.L., A.R. and D.S.; formal analysis, F.L..; investigation, A.R.; re-F.A.L.;
investigation,
sources, A.R.-M.;
F.L.; data resources,
curation, F.A.L.; data curation,
A.R.; writing—original A.R.-M.;
draft writing—original
preparation, draft preparation,
F.L.; writing—review and ed-
F.A.L.; writing—review and editing, A.R.-M.; visualization, F.A.L.; supervision, A.R.-M.; project ad-
iting, A.R.; visualization, F.L.; supervision, A.R.; project administration, F.L.; funding acquisition,
ministration,
A.R. F.A.L.;
All authors have funding acquisition,
read and agreed toA.R.-M. All authors
the published have
version of read and agreed to the published
the manuscript.
version of the manuscript.
Funding: This research was co-funded by the INTERREG V-A Cooperation, Spain-Portugal MAC
Funding: This research was2014-2020
(Madeira-Azores-Canarias) co-fundedprogram
by the INTERREG V-A Cooperation,
and the MITIMAC Spain-Portugal MAC
project (MAC2/1.1a/263).
(Madeira-Azores-Canarias) 2014-2020 program and the MITIMAC project (MAC2/1.1a/263).
Conflicts of Interest: The authors declare no conflict of interest.
Conflicts of Interest: The authors declare no conflict of interest.Membranes 2021, 11, 773 20 of 50
Appendix A. Microcontroller Source Code (ATmega328)
/*********************************************************************************************
*******
CSP_MCDI ATmega328 source code
Title: Design and implementation of an electrical characterization system for mem-
brane capacitive deionization units for water treatment.
Authors: Federico Leon, Alejandro Ramos-Martin and David Santana-Quintana.
**********************************************************************************************
******/
// V2-2021/07/07
#include
#include
#include
#include
// Configuracion nombres del sistema ADS y DAC
Adafruit_ADS1115 ads;
//Adafruit_MCP4725 dac;
Adafruit_MCP4725 dac1;
// Configuración de los reles para conseguir sistemas aislados
const int Rele1 = 2;//Rele de control 1.
const int Rele2 = 3;//Rele de control 2.
int16_t a;
int16_t b;
int c = 0; // Consigna para los ensayos
/************************************************************************************
* Inicialización de variables
************************************************************************************/
unsigned long inicio=0;//Variable de entrada que fuerza la puesta en marcha y parada
del ensayo.
// 0 -> En espera o parado.
// 1 -> Cargar con consigna de tension maxima.
// 2 -> Cargar con consigna de carga electrica.
// 3 -> forzar descarga con resistencia externa.
// 4 -> carga y descarga.
// 5 -> conductimetro.
unsigned long tiempo_1=0;//Tiempo de precarga.
unsigned long tiempo_2=0;//Tiempo de carga, cuando se establezca la referencia de
carga eléctrica (inicio=2).
unsigned long tiempo_3=0;//Tiempo de estado de auto-descarga o tiempo de man-
tenimiento de la tensión
unsigned long tiempo_4=0;//Tiempo de estado de descarga.
unsigned long tiempo_5=0;//Tiempo de estado de auto-descarga.Membranes 2021, 11, 773 21 of 50
uint16_t Vcmax=0;//Consigna de tensión máxima de carga, siempre se aplicará por
seguridad.
int estado=1;//Variable de salida que indica en que modo de operación se encuentra
la celda de CDI
// 0 -> En espera o stop, pero enviando datos.
// 1 -> En estado de precarga, durante tiempo_1.
// 2 -> En estado de carga, hasta que se complete el tiempo_2 o se alcance la tensión
Vcmax para evitar la
// electrolisis
// 3 -> En estado de auto-descarga.
// 4 -> Finalizado el ensayo.
unsigned long control_tiempos=0;//Variable de control de tiempos en cada estado.
/* RESOLUCIONES del MCP4725
* Tensiones del Arduino:
* 0 V > 2.5 V ——>> Tensiones positivas 0–2048 bit para MCP4725
* 2.5 V > 5 V ——>> Tensiones negativas 2048–4095 bit para MCP4725
*/
//Expresión de cálculo; NOTA: Vx4=Gain*(Vx2-Vard)+Voffset; Gain=1;Voffset=0;
/*
* Vx4=(Vx2-Vard)
*/
/*********************************************************************
* Ventrada[−2.5;2.5]V // Valores de entrada al OPA548
********************************************************************/
uint16_t Vcuenta1=0;//Vopa —->[X4=2.5 V]
uint16_t Vcuenta2=2048;//Vopa —->[X4=0 V]
uint16_t Icons=2048;//Consigna establecida de corriente de carga-descarga.
// Iconns es un valor inicial que luego se refresca
int16_t results;
int16_t results1;
/************************************************************************************
* Configuración del puerto serial y del timerone
************************************************************************************/
void setup()
{
Serial.begin(9600);
pinMode(Rele1, OUTPUT);
pinMode(Rele2, OUTPUT);
digitalWrite(Rele1, HIGH);//HIGH–> NC en el relé 1
digitalWrite(Rele2, HIGH);//HIGH–> CDI descargada (NC en el relé 2)
Timer1.initialize(100000);// Configuración del timerONE
Timer1.attachInterrupt(intu);// Asignación de la subrutina a la interrupción del
timerONE
dac1.begin(0 × 62); //Control de la corriente. Direccionamiento del conversor ADC
//dac.begin(0 × 63); //Control de la tensión. Direccionamiento del conversor ADC
ads.begin(); //Inicia el ADS1115.
ads.setGain(GAIN_ONE); // 1× gain +/− 4.096 V 1 bit = 2 mV 0.125 mV
// Establecimiento de la ganancia del ADCMembranes 2021, 11, 773 22 of 50
/*
* Ventrada[2,5;−2,5] –> Rcerámica=18 ohm
* I_carga_max=2.5/18=138,9 mA
* Icarga maxima=138.9 mA –> {Icons=0}
* Icarga mínima=−138.9 mA -> {Icons=4095}
*/
/************************************************************************************
* Configuración de los DAC y los relés
************************************************************************************/
dac1.setVoltage(2048, false);//Inicializado a 0A.
digitalWrite(Rele1, HIGH);//Rele NC
digitalWrite(Rele2, HIGH);//Rele NC
/*
* El OPA esta como un seguidor de tensión y la CDI está a tierra
*/
}
//interructión a los 1 micros
void intu()
{
Serial.print(a);
Serial.print(“,”);
Serial.print(b);
Serial.print(“,”);
Serial.print(Icons);
Serial.print(“,”);
Serial.print(Vcmax);
Serial.print(“,”);
Serial.println(estado);
// Serial.print(“,”);
// Serial.println(inicio);
control_tiempos=control_tiempos+1;
}
/***********************************************************************************************
* Se realizan los ensayos
***********************************************************************************************/
void loop(void)
{
Timer1.detachInterrupt();//Se deshabilita la interrupcion de envio de datos
switch (inicio){
//Tiempo a 0 sg
case 0: //Estado de espera o parada.
digitalWrite(Rele1, HIGH);//Relé NC.
digitalWrite(Rele2, HIGH);//Relé NC.
results1 = ads.readADC_Differential_0_1();
results = ads.readADC_Differential_2_3();
a = results1;
b = results;
control_tiempos=0;
Timer1.attachInterrupt(intu); //Se habilita la interrupción de envio de datos.
break;Membranes 2021, 11, 773 23 of 50
/*****************************************************************************************
* RESOLUCIONES del MCP4725
* Vard= 5 V − 2.5 V ——>> Tensiones positivas 4095–2048 bit para MCP4725
* Vard= 2.5 V − 0 V ——>> Tensiones negativas 2048–0 bit para MCP4725
******************************************************************************************/
case 1: //Carga con consigna de tensión máxima.
switch (estado){
case 1: //Forzar estado de precarga.
digitalWrite(Rele1, HIGH);//Rele abierto (NC)
digitalWrite(Rele2, HIGH);//Rele cabierto (NC)
//Tensión
//dac.setVoltage(4095, false);//Tensión en el OPA, X4= −2.5 V.
//Corriente
// Se le asigna un ‘0’ al OPA
dac1.setVoltage(2048, false);//Corriente en el OPA, X4= 0 A.
results1 = ads.readADC_Differential_0_1();
results = ads.readADC_Differential_2_3();
a = results1;
b = results;
if(control_tiempos>=tiempo_1){
estado=2;
control_tiempos=0;
}
Timer1.attachInterrupt(intu); //Se habilita la interrupción de envio de datos.
break;
case 2: //Forzar estado de carga sólo con límite de tensión.
// Estado de carga, hasta que se complete el tiempo_2 o se alcance la
// tensión máxima
digitalWrite(Rele1, LOW);//Relé abierto (NA).
digitalWrite(Rele2, LOW);//Relé abierto (NA).
//
dac1.setVoltage(Icons, false);//Falta asignar la corriente.
//
//dac.setVoltage(Vcuenta1, false);//Falta asignar la tensión.
results1 = ads.readADC_Differential_0_1();
results = ads.readADC_Differential_2_3();
a = results1;
b = results;
// Valor máximo de tensión 1,2 V o 1 V para evitar la electrolisis de la CDI
if (a > Vcmax) {
estado=3;//Estado de auto-descarga
control_tiempos=0;
digitalWrite(Rele1, HIGH);//Relé NC.
digitalWrite(Rele2, HIGH);//Relé NC.
// Corriente
dac1.setVoltage(2048, false);//corriente en el OPA, X4= OA. Se le
// asigna un ‘0’ al OPAMembranes 2021, 11, 773 24 of 50
// Tensión
//dac.setVoltage(4095, false);//Tensión en el OPA, X4= −2,5 V.
}
Timer1.attachInterrupt(intu); //Se habilita la interrupción de envio de datos.
break;
case 3://Forzar estado de auto-descarga.
results1 = ads.readADC_Differential_0_1();
results = ads.readADC_Differential_2_3();
a = results1;
b = results;
if(control_tiempos>=tiempo_3){
//Tiempo_3–> Tiempo de estado de auto-descarga
estado=4;//Ensayo finalizado
inicio=0;
control_tiempos=0;
}
Timer1.attachInterrupt(intu); //Se habilita la interrupción de envio de datos.
break;
}
//Fin del switch (estado)
break;
case 2://Carga con consigna de carga eléctrica.
switch (estado){
case 1: //Forzar estado de precarga.
digitalWrite(Rele1, HIGH);//Rele NC.
digitalWrite(Rele2, HIGH);//Rele NC.
//
//dac.setVoltage(4095, false);//Aproximadamente en el OPA, X4= −2.5 V.
//
dac1.setVoltage(2048, false);//Aproximadamente en el OPA, X4= 0 A.
results1 = ads.readADC_Differential_0_1();
results = ads.readADC_Differential_2_3();
a = results1;
b = results;
if(control_tiempos>=tiempo_1){
estado=2;
control_tiempos=0;
}
Timer1.attachInterrupt(intu); //Se habilita la interrupción de envio de datos.
break;
case 2://Forzar estado de carga con limite de tiempo 2.You can also read
